There has been a recent and justified resurgence in interest in the use of oncolytic viruses for cancer therapy, primarily due to highly promising Phase II data with at least three different viral strains and recent early Phase III data. It is noteworthy that multiple vectors currently undergoing randomized trials express a cytokine to enhance their therapeutic effects, and have been reported to induce anti-tumor immunity. However, the immunotherapeutic potential of this platform remains under-developed. We have demonstrated both in pre-clinical models and in the clinic that oncolytic vaccinia can raise protective immunity against tumor antigens. Indeed, under some circumstances oncolytic vaccinia provides potent anti-tumor effects entirely through immunotherapeutic mechanisms of action. However, while the powerful immunogenicity of vaccinia is appreciated and relatively well understood from its use as a vaccine, the current oncolytic strains have not been designed to take advantage of this potential. We therefore propose to develop next generation vectors that act as potent and specific immunotherapeutics. Importantly we will look to do this without deleteriously affecting their directly oncolytic capabilities. It is believed that the logical desin of viral vectors to both replicate selectively in cancer cells and direct a specific and targeted immune response against the tumor will significantly enhance their therapeutic potential, and represents a novel treatment platform we have termed Immuno-Oncolytic Viruses (IOV). Optimization of immunotherapeutic effects will be achieved through inter-related approaches acting at a global level and at multiple steps in the immune response. Initially, we will incorporate technologies pioneered in the development of vaccine therapies to selectively modulate TLR activation and the innate immune response and apply these to oncolytic vaccinia. By re-directing, rather than simply activating innate immune pathways it is possible to modulate the overall immune response without deleteriously affecting viral oncolytic activity. Secondly, we will manipulate immune-modulatory virulence genes encoded by vaccinia in order to re-direct the naturally Th2-weighted immune response raised by vaccinia towards the potentially more beneficial Th1 arm. Finally, the expression of specific antigens will be used to boost the immune targeting of the bulk tumor and of specific subsets of cells within the tumor, notably tumor initiating cells. The vectors produced in this work will become next generation therapeutics with predefined immunotherapeutic mechanisms of action and significantly enhanced anti-tumor effects. They will undergo (independently funded) GMP manufacture over the same time frame as this work and so be ready for immediate clinical testing by the completion of this study and incorporating treatment regimens developed within this application.